Apparatus for detecting unprepared postage stamps

ABSTRACT

There is disclosed an optical arrangement for detecting regular, non-specially-prepared postage stamps for machines which accordingly face or orient the articles for automatic sorting. Detection is limited to the serrated edges common to all existing stamps, which serrations may easily be made into a code. A light source is arranged to impinge radiation at an acute angle relative to the direction of document travel. Thereby the sides of the serrations parallel to this direction are highly illuminated. A photoelectric sensor receives the train of light pulses emitted by the sides of the stamp serrations, which are fed to an amplifier and on to a pulse counting circuit, which serves to operate a deflector.

1451 Dec. 18, 1973 APPARATUS FOR DETECTING UNPREPARED POSTAGE STAMPS[76] Inventor: Heinz Hudler, Ketzergasse 389,

Vienna, Austria 221 Filed: Mar. 21, 1972 211 Appl. No.: 236,619

[30] Foreign Application Priority Data Mar. 30, 1971 Austria A 2691/71[52] US. Cl ..250/555, 250/223 R, 209/DIG. 1 [51] Int. Cl. G01n 21/30[58] Field of Search 250/219 DO, 219 DR, 250/219 LG, 222 PC, 223 R;209/111.5,

DIG. l

[56] References Cited UNITED STATES PATENTS Mustert 250/219 DOStegenga.. 250/222 X PC Frankie et a1 250/223 R 3,313,944 4/1967 Muir250/219 LG 3,488,511 l/1970 Mori et al. 250/219 DO 1 2,936,886 5/1960Harmon 250/219 DQ Primary Examiner-Wa1ter Stolwein Att0rne vC. CornellRemsen, Jr. et a1.

57 ABSTRACT There is disclosed an optical arrangement for detectingregular, non-specially-prepared postage stamps for machines whichaccordingly face or orient the articles for automatic sorting. Detectionis limited to the serrated edges common to all existing stamps, whichserrations may easily be made into a code. A light source is arranged toimpinge radiation at an acute angle relative to the direction ofdocument travel. Thereby the sides of the serrations parallel to thisdirection are highly illuminated. A photoelectric sensor receives thetrain of light pulses emitted by the sides of the stamp serrations,which are fed to an amplifier and on to a pulse counting circuit, whichserves to operate a deflector.

10 Claims, 10 Drawing Figures PAIENIEDHH: 18 ms sum 201 2 APPARATUS FORDETECTING UNPREPARED POSTAGE STAMPS The automatic distribution ofletters in highly mechanized routing post offices basically involvesvarious operations. Those of the received letters must be sorted outwhich have a unhandly size because they are too large, too thick or toostiff to be handled by machine (separation of sizes). The remaining mailitems are then turned around and turned over so that the postage stampson all letters are on the same side and have the same orientation. Thisoperation involved in the handling by machine is referred to as thefacing of the letters and is carried out with so-called facing machines.Only mail items which have been faced can be marked by machine andtransferred to the actual automatic sorting operation.

The facing of the letters by machine involves the searching for anddetection of the postage stamps. The optical methods presently used toidentify postage stamps do not give satisfactory results. For thisreason, postage stamps have been prepared by being provided withdetectable marks. Various methods have been developed for this purpose.Of these methods, one of the most reliable ones involves the use ofluminescent post age stamps. The paper of the postage stamps isimpregnated or coated with fluorescent or phosphorescent dyestuff sothat the stamps can be relatively easily detected when irradiated withultraviolet light (quartz lamp) and simple indicating methods can beemployed. In this method, the percentage of errors is low (about 1percent). In other processes, the finished postage stamp is providedwith a luminescent coating, or specific spectral colors are used in thestamp picture and can be screened out with the aid of special filtersand indicated.

All these methods have the disadvantage that the additional preparationprocesses add considerably to the costs of making the postage stamps sothat the saving of costs which is desired by the use of facing machinesmay be offset. Another disadvantage resides in that the preparation ofthe stamps adversely affects the purity of their colors. For instance,the colors of the stamp picture may not give the desired impression onthe luminescent base, or the preparation may adversely affect thequality of the stamp paper or may stain the same. The method which ismost widely used and involves the use of fluorescent postage stamp paperhas a serious technical disadvantage residing in that many of theenvelopes being used are made from a paper which has been renderedhighly fluorescent by an addition of so-called brighteners. Postagestamps stuck onto such envelope cannot be detected with simple means.For the reasons set forth, the postal administrations in a number ofcountries have not adopted such methods,

code and by means of modern machines can be made exactly with thedesired pitch.

The invention provides an apparatus for identifying normal, serrated,unprepared postage stamps on letters by machine, which apparatuscomprises a light source, which illuminates at a small angle the lettersmoved in a given direction, and a photoelectric sensor, and ischaracterized in that the light source is arranged so that the lightrays include an acute angle with the direction of travel and the stampsare thus laterally illuminated with grazing light in such a manner thatthe sides of the serrations on the stamp sides which are parallel to thedirection of travel are highly illuminated, and the pho toelectricsensor, which receives a train of light pulses emitted by the sides ofthe serrations of the passing stamps, is connected to a thresholdamplifier, which has an optimum gain in a range which is adjustable toinclude the frequency of the serrations passing the sensor, whereas theoutput of the amplifier is connected by a timer or by a pulse-countingcircuit to a known switch, which serves, e.g., to operate a deflectorfor selecting a route for each letter.

Because the location at which the stamp is stuck on the envelope is notpredetermined, a relatively wide strip must be scanned. For this reason,the photoelectric sensor consists, in accordance: with the invention, ofone or more photoelectric cells provided with a slit, or of one or morephotoelectric cells provided with an optical system which comprises atleast two cylindrical lenses having longitudinal axes at an angle of toeach other.

A plurality of photoelectric cells are provided, if desired, incombination with a selector circuit which onsures that only thatamplifier channel which carries the useful signal is used to operate theswitch.

According to a further feature of the invention, the transient time ofthe selective amplifier is selected so that an audio-frequency signalvoltage which is sufficient to initiate the switching operation will notbe generated until the scanning operation has been performed for a timewhich is approximately one-half of the time for a stamp to pass.

An imporatant feature of the invention resides in that strong grazinglight is used for scanning so that the apices and sides of theserrations are particularly brightly illuminated. This optimum effectcan easily be obtained if the light source is adjustable and thephotoelectric arrangement is rotatable and pivotally movable.

The principle underlying the invention affords the advantage that onlythe postage stamps, and of these only the serrations, are sensed,whereas there is no photoelectric respouse to disturbing imprints, marksand the like.

If the stamps are provided with serrations differing in pitch, independence on the value of the stamps, the provision of a plurality ofselective amplifiers, which are tuned to suitable frequencies, willenable a check as to the value of the postage stamps or a sorting forother considerations.

Further features and advantages of the invention will become apparentfrom the following description with reference to the drawing, in whichFIG. 1 is a side elevation showing the apparatus according to theinvention,

FIGS. 2a, 2b and 2c show different embodiments of the photoelectricsensor,

FIG. 3 shows the limits of the area in which a postage stamp should bestuck on a letter,

FIG. 4 shows how a plurality of photoelectric sensing units may be usedto scan a wide strip,

FIGS. 5a, 5b and 5c represent the transients of the selective amplifierin response to different signals and FIG. 6 illustrates the mostdesirable adjustment of the photoelectric sensor.

As is apparent from FIG. I, the overall arrangement comprises a beltconveyor 1, by which the letter 2, on which a postage stamp has beenstuck, is moved at a constant velocity v under the photoelectric sensor4. The light source 3 must illuminate the letter and the stamp bystrongly grazing light so that only the uneven portions of the surfac ofthe letter, particularly the stamp with its serrations, are scanned. Inresponse to the scanning of the serrations, the photoelectric sensorgenerates an audiofrequency pulse train, which is amplified by aselective amplifier 5 and, when a certain threshold value is exceeded,the amplified pulse train is delivered to a timer 6 or to apulse-counting circuit 7.

In the drawing, both possibilities are provided for (changeover switchesU U In practice, however, no change-over will be provided for and onlyone means or the other will be employed. When the serrations of a stampare being scanned and the threshold value has been reached and thethreshold value of the output voltage of the amplifier has beenmaintained for a predetermined, short time, the timer or thepulse-counting circuit will cause an operation of the switch 8.

As is shown in section in FIG. 2a, the scanning may be accomplished inthe simplest case by means of a photoelectric cell 9 and a slit 10,which has a small width, e.g., of 0.5 millimeter, and a longitudinalaxis extending parallel to the illuminated sides of the serrations. Inthis case, the photoelectric sensor must be disposed very close to thepostage stamp so that the sensor can receive a sufficiently large amountof reflected light from the serrations 11. For this reason, provisionmust be made in connection with the conveyor to ensure that that surfaceof the letter which is to be scanned is always at the same distance fromthe photoelectric sensor, regardless of the thickness of the letter.This disadvantage may be avoided by the provision of an optical systembetween the postage stamp and the photoelectric cell (FIGS. 2b and Thisoptical system consists of at least tow cylindrical two one of which(14), forms on the photoelectrical cell 9 an image corresponding to thescanning width (one serration of the postage stamp) whereas the secondlens (13) has a longitudinal axis at an angle of 90 to that of the firstlens and results in a reduction so that an image correspnding to thewidth of the scanning strip is formed on the photoelectric cell. Thelongitudinal axes of the cylindrical lenses are, respectively, paralleland at right angles to the illuminated sides of the serrations. FIGS. 2band 20 show the light pahts in two section planes which extend throughthe optical axis at an angle of 90 to each other.

An aperture plate 12 disposed in front of the photoelectric cellcooperates with the cylindrical lens system like a slit in conjunctionwith a normal optical system comprising spherical lenses. With thismethod, the distance between the postage stamp and the photoelectricsensor can be much increased so that the variations of the distancebetween the postage stamp and photoelectric cell which are due to thethickness differences between the letters can be neglected and a widerstrip of the letter can be scanned.

In accordance with an international agreement, the postage stamp shouldbe stuck in an area having dimensions L 74 millimeters and B 40millimeters at the upper right corner of the letter, as is shown in FIG.3 Depending on the size of the stamp, there is a certain latitude as tothe location of the stamp in this area. To ensure that the serrations atthe upper edge of the stamp can be reliably scanned, the photoelectricsensor must cover a strip having a width H of approximately 15millimeters. This requirement cannot easily be met with a singlephotoelectric cell. It is more desirable to provide a plurality ofphotoelectric cells in an arrangement as shown in FIG. 4. In view oftheir overall dimensions, the photoelectric sensing units 15 arestaggered. The resulting scanning time differences are insignificant forthe detecting operation. Because there may be interference in theoverlap areas, the spacing d of the photoelectric cells in the directionof travel is an integral multiple of the pitch of the serrations to bescanned. The outputs of the photoelectric cells are connected by theamplifier channels 16 to a selector circuit 17, such as an OR gate. Thisselector circuit connects only that amplifier channel to the switch 8which carries a signal in response to the scanning of a postage stamp.As a result, any interference signals in the other channels are notadded but entirely eliminated.

If a postage stamp being scanned travels at a speed of, e.g., 2.5 metersper second and its serrations have a pitch of, e.g., 1.4 millimeters,the pulse train received by the selective amplifier will have afrequency f 2500/ l .4 I785 Hz. In this case, the scanning time for astamp having a width of, e.g., 25 millimeters is T 25/2500=0.01 second10 milliseconds. The voltage waveform at the output of the selectiveamplifier is represented in FIG. 5a and determined by the transientresponse of this amplifier. The selected transient time T, is aboutone-half of the scanning time T (t 5 milliseconds). In this case theamplifier may have a bandwidth B which is approximately l/T 200 Hz. Inthis case, the selective amplifier has a Q factor which is equal to1785/200 9. Whereas the threshold value of the amplifier is reached atpoint A, the switch will not yet be operated. Only when the thresholdvalue has been maintained or exceeded for a certain time, for instance,Ta/2 5 milliseconds, and point B has been reached does the switch 8respond. This requirement may be met by a timer, which comprises arectifier for the audio-frequency output pulses and a variableintegrating resistance-capacitance circuit, or by a circuit 7, which atthe time when the threshold voltage has been reached begins to count apresettable number of output pulses and only thereafter operates theswitch 8. It is apparent from FIG. 5b that short interferences withinthe useful frequency range will remain below the threshold voltage andwill not even reach the point A. FIG. 5c shows that short interferencepulses which are very strong will reach the point A but will not reachthe point B so that the switch will not respond in this case too. Forthis reason, the edges of the letters and the uneven portions of thepaper are not indicated because they result in signals which have aduration which is shorter than the scanning time of a postage stamp orhave a frequency which differs from the audiofrequency of the voltagewaveform generated by the serrations.

The function of the apparatus according to the invention for thedetection of postage stamps depends highly on the illuminating device.To ensure a correct illumination with grazing light, the light source isadjustable so that the angle of incidence of the light rays on the planeof the letter or the angle included by the light rays and the directionof travel can be adjusted. Because under suitable illumination theapices and sides of the several serrations of the postage stamps forminclined bright lines rather than dots, the photoelectric sensor is alsorotatable about its optical axis. It is apparent in FIG. 6 that theilluminating device L can be rotated through about 30 opposite to thedirection of travel F to provide for a particularly bright illuminationof the sides of the serrations and a generation of the strongest lightpulses. In this case, the photoelectric sensor 18 must be rotatedaccordingly. Because the strongest reflection from the illuminatedserrations will not be at right angles to the plane of the letter, theangle between the optical axis of the photoelectric sensor and the planeof travel should also be adjustable.

I claim:

1. Apparatus for detecting normal, serrated, unprepared postage stampson documents moving in a given direction, comprising light source meansarranged for emitting a single beam of light radiation obliquelydirected at an acute angle along the direction of travel of thedocuments and highly illuminating the sides of the serrations only whichare associated to a side of the stamps which is substantially parallelto the direction of travel of the documents, photoelectric sensing meansstationarily arranged relative to the moving documents for receiving thelight emitted by said sides of said serrations, which received light isin the form of a train of pulses corresponding to the serrated stampparallel edges moving relative to the light source beamed radiation,threshold amplifying means coupled to said sensing means, saidamplifying means being arranged to have an optimum gain. in a rangewhich is adjustable to include the frequency of the serrations passingsaid sensing means, and first means coupled to said amplifying means forreceiving the output of the latter and deriving therefrom a controloutput signal which characterizes the positional orientation of thestamp on its associated document.

2. The apparatus according to claim 1 wherein said photoelectric sensingmeans includes at least one photoelectric cell provided with a slithaving a longitudinal axis which is parallel to the illuminated sides ofthe serrations.

3. The apparatus according to claim 1 wherein said photoelectric sensingmeans includes at least one photoelectric cell directed to receive saidlight pulse train, a pair of cylindrical lenses having longitudinal axeswhich are arranged at an angle of to each other and extend,respectively, parallel and at right angles to the illuminated sides ofthe serrations, and an aperture plate disposed proximate saidphotoelectric cell.

4. The apparatus according to claim 1 wherein said photoelectric sensingmeans includes a plurality of photoelectric cells arranged in a row,said cells having in the direction of travel a predetermined spacing (d)from one another which is an integral multiple of the pitch of the stampserrations, and further including se lective amplifier means coupled tosaid plurality of photoelectric cells and having a plurality ofamplifier channels, and selector circuit means coupled to said so lectoramplifier means for connecting only that amplifier channel which carriesthe useful output to said first means.

5. The apparatus according to claim 2 wherein said threshold amplifyingmeans is designed such that the transit time thereof is substantiallyone-half of the time for a moving stamp to pass said photoelectricsensing means.

6. The apparatus according to claim 2 wherein said first means iscomprised of a timer arrangement which includes a rectifier and anintegrating resistancecapacitance circuit for initiating a controlledoutput only when a received output from said amplifying means, asderived from an input to the latter which is sufficient for aninitiation, has been maintained for a predetermined adjustable time.

7. The apparatus according to claim 2 wherein said first means iscomprised of a pulse counting circuit for initiating a controlled outputwhen the photoelectric sensing has resulted in the generation of apredeterminable adjustable number of pulses after the threshold voltageof said amplifying means has been reached.

8. The apparatus according to claim 1 wherein said light source means isarranged such that the output angle formed by the light rays with thedirection of document travel is adjustable.

9. The apparatus according to claim 8 wherein said photoelectric sensingmeans is rotatable about its optical axis.

10. The apparatus according to claim 9 wherein the angle included by theoptical axis of said photoelectric sensing means with the plane ofdocument travel is predeterminably adjustable.

1. Apparatus for detecting normal, serrated, unprepared postage stampson documents moving in a given direction, comprising light source meansarranged for emitting a single beam of light radiation obliquelydirected at an acute angle along the direction of travel of thedocuments and highly illuminating the sides of the serrations only whichare associated to a side of the stamps which is substantially parallelto the direction of travel of the documents, photoelectric sensing meansstationarily arranged relative to the moving documents for receiving thelight emitted by said sides of said serrations, which received light isin the form of a train of pulses corresponding to the serrated stampparallel edges moving relative to the light source beamed radiation,threshold amplifying means coupled to said sensing means, saidamplifying means being arranged to have an optimum gain in a range whichis adjustable to include the frequency of the serrations passing saidsensing means, and first means coupled to said amplifying means forreceiving the output of the latter and deriving therefrom a controloutput signal which characterizes the positional orientation of thestamp on its associated document.
 2. The apparatus according to claim 1wherein said photoelectric sensing means includes at least onephotoelectric cell provided with a slit having a longitudinal axis whichis parallel to the illuminated sides of the serrations.
 3. The apparatusaccording to claim 1 wherein said photoelectric sensing means includesat least one photoelectric cell directed to receive said light pulsetrain, a pair of cylindrical lenses having longitudinal axes which arearranged at an angle of 90* to each other and extend, respectively,parallel and at right angles to the illuminated sides of the serrations,and an aperture plate disposed proximate said photoelectric cell.
 4. Theapparatus according to claim 1 wherein said photoelectric sensing meansincludes a plurality of photoelectric cells arranged in a row, saidcells having in the direction of travel a predetermined spacing (d) fromone another which is an integral multiple of the pitch of the stampserrations, and further including selective amplifier means coupled tosaid plurality of photoelectric cells and having a plurality ofamplifier channels, and selector circuit means coupled to said selectoramplifier means for connecting only that amplifier channel which carriesthe useful output to said first means.
 5. The apparatus according toclaim 2 wherein said threshold amplifying means is designed such thatthe transit time thereof is substantially one-half of the time for amoving stamp to pass said photoelectric sensing means.
 6. The apparatusaccording to claim 2 wherein said first means is comprised of a timerarrangement which includes a rectifier and an integratingresistance-capacitance circuit for initiating a controlled output onlywhen a received output from said amplifying means, as derived from aninput to the latter which is sufficient for an initiation, has beenmaintained for a predetermined adjustable time.
 7. The apparatusaccording to claim 2 wherein said first means is comprised of a pulsecounting circuit for initiating a controlled output when thephotoelectric sensing has resulted in the generaTion of apredeterminable adjustable number of pulses after the threshold voltageof said amplifying means has been reached.
 8. The apparatus according toclaim 1 wherein said light source means is arranged such that the outputangle formed by the light rays with the direction of document travel isadjustable.
 9. The apparatus according to claim 8 wherein saidphotoelectric sensing means is rotatable about its optical axis.
 10. Theapparatus according to claim 9 wherein the angle included by the opticalaxis of said photoelectric sensing means with the plane of documenttravel is predeterminably adjustable.